Telemetry transmitters provide a convenient means for remotely monitoring the medical condition of a patient, i.e., monitoring heart related electrical signals, such as electrocardiogram (EKG) and cardiac pacemaker signals. The telemetry transmitter is connected to the patient by electrodes and wires. The telemetry transmitter includes terminals for receiving the EKG and pacemaker signals from the wires, and a wireless transmitter that comprises, for example, a radio frequency (RF) link. Additional circuitry may be provided in the transmitter device for amplifying, filtering and multiplexing the received EKG and pacemaker signals. The transmitter sends the EKG and pacemaker signals to a telemetry receiver, which is typically in a central station.
It is often desirable to monitor the EKG and pacemaker signals locally. For example, a doctor or nurse may wish to review the EKG and/or the pacemaker signals while making his or her rounds. In some Telemetry transmitters, such as the model 1481T Telemetry transmitter manufactured by the Siemens Corporation, a display is provided for locally monitoring the EKG signals. Although this provides convenience, it increases the cost of the telemetry transmitter.
An alternative method that allows local monitoring is to place a telemetry receiver in the patient's room and connect the telemetry receiver to a monitor, as is done at the central station. While convenient, this is also quite expensive. U.S. Pat. No. 3,882,277 to DePedro et al. describes such a telemetry system. A telemetry receiver is placed in the patient's room, and the receiver is connected to a modem for transmission over a conventional telephone system.
If the hospital has an EKG monitor available (for example, a mobile transport monitor), the EKG electrodes that are attached to the patient could be disconnected from the telemetry transmitter and reconnected to the transport monitor for in-room monitoring. This method is cost effective, but is inconvenient, because the patient's EKG signal is not received at the central station while the EKG electrodes are connected to the transport monitor. This method also requires that the caregiver perform four steps including: (1) disconnecting the electrodes from the telemetry transmitter; (2) connecting the electrodes to the transport monitor; (3) disconnecting the electrodes from the transport monitor, when local monitoring is completed; and (4) reconnecting the electrodes to the telemetry transmitter. Performing these steps takes up the caregiver's valuable time.
Another problem associated with the method described above could occur while monitoring the quality of the electrode contacts. The quality of the EKG and pacemaker waveforms is affected by the quality of the electrode contact to the skin, so viewing the EKG and/or pacemaker waveforms from the bedside monitor via the telemetry transmitter allows evaluation of the electrode contact in the patient's room. Using the method described in the previous paragraph, the electrode contact may be disturbed while performing steps (3) and (4). The caregiver would not immediately become aware of this problem because he or she would no longer be viewing the waveform on the transport monitor. The discrepancy would not be detected until someone viewed the waveform back at the central station. At that point, it would be necessary to dispatch another person back to the patient's room to fix the electrode contact.
A convenient, low cost apparatus for locally monitoring the output of an EKG telemetry transmitter is desired.